1. Field of the Invention
The present invention relates to a driving apparatus for a recording head or beads capable of ejecting inks of different colors, applicable to a color inkjet printer or the like, and also relates to an image recording apparatus including the driving apparatus.
2. Description of Related Art
Color inkjet printers are generally classified into two types. The first type has a single recording head including nozzle rows corresponding to the respective colors, for example, four colors of yellow (Y), magenta (M), cyan (C), and black (B). The second type has recording heads corresponding to the respective colors. Actuators are provided so as to correspond to the respective nozzles. Inks are ejected through nozzles by driving the corresponding actuators.
In printers of the above constructions, if a large number of actuators corresponding to the respective nozzles are driven at the same time, there may arise a problem of overcurrent or crosstalk. To relieve the problem, JP-A-5-138900 discloses a technique in which timings for supplying drive signals to actuators are staggered little by little. More specifically, a timing generator block generates waveform signals in which timings of rising edges of pulses are staggered from one another. Each recording head selects one of the waveform signals to be used as a drive signal for the actuators of the recording head. In this manner, the actuators of each recording head can be driven at timings different from the actuators of the other recording heads. The above problem can be relieved thus.
On the other hand, in recent years, for tone control and hysteresis control, a technique is adopted in which waveform signals different from one another in shape for one dot are selectively used as actuator driving signals, as disclosed in JP-A-2000-158643. The hysteresis control is for relieving a problem in which vibration upon driving an actuator remains to affect the later driving operation. More specifically, a waveform signal to be used to form a present dot is selected depending on the absence or presence of a dot immediately before and/or after the present dot. In this technique, the waveform signals for forming one dot differ from each another in the number of pulses, pulse width, pulse height, and the like. For example, the various numbers of pulses for one dot can vary the number of ink ejections for one dot and therefore the total quantity of dropped ink for one dot. This can realize tone control. On the other hand, the various widths of pulse to form one dot, for example, can realize hysteresis control.
In the former of the above-described two techniques, waveform signals generated in the timing generator block are identical in the number of pulses for one dot, and pulse width, and pulse height. The waveform signals differ from one another only in timing of rising edge of pulse. In the former technique, therefore, tone control and hysteresis control are impossible.
In the latter of the above-described two techniques, waveform signals are repeatedly output at constant intervals and the waveform signals themselves are used as timing signals for driving actuators. Therefore, if this technique is applied to a color printer and each color recording head is intended to be time-divisionally driven like the former technique, the waveform signals must be supplied to each recording head. As a result, a great number of signal lines are required between the recording heads and the printed circuit board in the printer body. This brings about a problem of difficulty of routing of the signal lines. In addition, there may arise problems of increasing the manufacturing cost of the printer and complicating the construction.